This invention relates in general to miniaturized fuse devices and, more particularly, to such an arrangement which is specifically designed for, and mounting on, printed circuit boards and the like.
In the past, when fuse devices are necessary for circuitry on the printed circuit (PC) board, the most common practice has been to utilize the more well known glass tube type device which is cylindrical in shape with two metal caps at each end and having a glass tube in between in which a fuse element is longitudinally positioned. To maintain the fuse device on the PC board, separate lock-in terminal devices must be employed and mounted to surface area in which the glass tube fuse may be snapped in place at respective ends and retained therein.
There are several undesirable features concerning the utilization of these glass tube fuses in conjunction with the printed circuit board application. They take up much too much space relative to the PC board itself. They are somewhat difficult to insert in their associated end terminals. Being in large part constructed of glass, they are inherently fragile and if broken may be dangerous to an individual attempting to remove them from their terminal holders. Indeed, to use the fingers to attempt removal of the fuse device under any circumstances subjects the individual to a shock hazard as long as the surrounding circuitry is energized. For safe removal, a specialized, non-metallic tool is required.
One additional drawback to the glass tube fuse is its cost. In order that the associated end terminals retain their required spring tension capability over the expected service life, high tensile material, such as heat treated copper or copper-berillium alloy must be used, thereby contributing to high manufacturing costs. Moreover, the end terminals are difficult to properly attach to the PC board by the conventional wave soldering process. They frequently move or shift in location during the wave soldering process causing difficulty for later use.
There are, of course, alternatives to the cylindrical glass tube fuse device. One such alternative is a blade type fuse such as that shown at 14 in FIG. 2. It is highly compact, easy to grasp with the fingers at a location electrically isolated from shock and designed for convenient insertion and removal without special tools. This blade fuse device has a major application in automotive environments and is intended to plug in to a central connector block with other devices under the dash or the like. The problem with this blade fuse and others of its type is that it is not designed for application on PC boards. Not only must there be an associated holder arrangement for individual fuses, but the holder must be such as to hold firm during wave soldering applications but at the same time be easily mounted before being permanently attached to the board, and other considerations.